In networks, such as core networks that transfer information among multiple regions and metro networks that transfer information within a region, the Optical Transport Network (OTN) has been used, which is a standard for optical transmissions, and is recommended by the International Telecommunication Union Telecommunication Standardization Sector (ITU-T).
The OTN enables a wide variety of client signals, such as synchronous digital hierarchy/synchronous optical network (SDH/SONET) signals, Ethernet® signals, time division multiplexing (TDM) signals, to be accommodated into OTN frames, e.g., optical channel payload units (OPUs), optical channel data units (ODUs), and optical channel transport units (OTU), for transmission.
In recent years, traffics have surged in access networks which aggregate into core networks (or metro networks).
Under such backgrounds, in order to accommodate signals from an access network into a core network (or a metro network), techniques have been demanded, which can efficiently accommodate signals in different bands (bit rates), such as SDH/SONET signals, Ethernet® signals, TDM signals, into OTN frames.
As an example of such techniques, multiplication of ODU frames was stipulated by the ITU-T. Further, ODU flex frames which can accommodate client signals in a unit of 1.25 Gbps are also stipulated (refers to Non-Patent Reference 1 listed below).
Patent Reference 1 listed below discloses a technique wherein OTN frames standardized by the ITU are uniformly applied, independently of the types of signals to be accommodated, and the signals are accommodated in SDH/SONET frames, which have been standardized by the ITU correspondingly to OTN frames.
Patent Reference 2 listed below discloses a technique wherein specialized framing and encoding are executed on SONET/SDH signals and 10 Gb E-WANPHY signals, and the bit rates of the SONET/SDH signals and 10 Gb E-WANPHY signals are adjusted to the bit rates equivalent to those of 10 Gb E-LANPHY signals, followed by transparently mapping these signals to a single wavelength for WDM signals, for transmitting the mixed signals.
In addition, Patent Reference 3 listed below discloses a technique wherein transmission data is mapped to a payload region while relating it to the identifier of an overhead region on the transmission side, while reassembling received data from the payload region, using the identifier, on the reception side.
Further, Patent Reference 4 listed below discloses a technique wherein, upon accommodating the frequency deviation exceeding the frequency deviation that can be accommodated by NJO bytes, the data corresponding to the frequency deviation exceeding the frequency deviation accommodatable by NJO bytes is stored in FS bytes defined in an OTU frame.    Patent Reference 1: Japanese Laid-open Patent Publication No. 2008-227995    Patent Reference 2: Japanese Laid-open Patent Publication No. 2008-92130    Patent Reference 3: Japanese Translation of PCT International Application No. 2004-523959    Patent Reference 4: Japanese Laid-open Patent Publication No. 2008-113394    Non-Patent Reference 1: Interfaces for the Optical Transport Network (OTN), ITU-T (International Telecommunication Union Telecommunication Standardization Sector), Recommendation G.709
Client signals are accommodated in tributary slots (TSs) located in a payload region in an OTN frame.
Such TSs, however, are merely designed for accommodating client signals being propagated between Ethernet® physical ports.
In other words, TSs are not designed for accommodating client signals being propagated between virtual ports defined using Layer 2 Identifiers, such as a virtual local area network (VLAN).
Hence, TSs under the current standard can accommodate client signals in a unit of 1.25 Gbps at the minimum, and accordingly, client signals cannot be accommodated flexibly and efficiently, free from the limitation of the unit of 1.25 Gbps.
For example, a client signal in a band smaller than 1.25 Gbps cannot be accommodated and multiplied in an OTN frame.